In the presentation, I reviewed the valuation multiples of several hot tech companies--the ones folks usually point to when citing evidence that there's a new tech bubble. These companies included Facebook, Zynga, Groupon, and Twitter.

The valuation of most of these companies is actually reasonable on a revenue and earnings basis, at least as far as I can tell. Of the four, Twitter's valuation seems by far the most speculative, especially since the company has yet to build a major business model.

Specifically, at a private-market valuation of around $7 billion on what I estimated at $250 million of 2011 revenue, Twitter is trading at about 30-times this year's revenue. That valuation is fairly described as "aggressive."

As soon as I published the presentation, however, someone closer to the company pinged me to say that Twitter's revenue this year will be closer to $100 million than $250 million.

And that led me to check with someone who is actually privvy to Twitter's financials. This person estimated that Twitter's revenue for 2011 will likely be in the $140 million range -- $100 million of ad revenue and another $40 million or so of data revenue.

But $140 million of revenue is a ways from $250 million of revenue, especially when one's valuation is $7 billion.

Specifically, it's a multiple of 50-times revenue.

Now, Twitter is still growing very fast, especially when measured by number of sign-ups. (The number of active users appears to be far smaller). And Twitter is just at the beginning of developing a real revenue model. And it's possible that, when Twitter really stomps on the revenue gas, its revenue will quickly jump to, say, $500 million, which would make a $7 billion valuation more reasonable.

On the other hand, it's also possible that Twitter will never find a great business model, in which case its revenue will just muddle along. (And, in which case, its valuation is seriously overstretched).

In any event, I asked a Twitter investor what the Twitter investor thought of Twitter's current private-market valuation.